<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    // 回调函数的this指向 一定要去阅读文档！！！
    setTimeout(function (){
        console.log(this)
    },2000)

</script>
</html>